Initiating device for suspended explosive charges



May 6, 1952'v w.-s. SWEETMAN INITIATING DEVICE FOR SUSPENDED EXPLOSIVECHARGES Filed March 2, 1948 W. G. SWEETMAN Patented May 6, 1952INITIATING DEVICE FOR SPENDED EXPLOSIVE CHARGES William G. Sweetman,Houston, Tex.

Application March 2, 1948, Serial No. 12,544

6 Claims.

This invention relates to a device for detonating explosives andparticularly to a device for use as an initiator for setting offexplosive charges in a well.

In my co-pending application, Serial No. 721,433, filed January 10,1947, now Patent No. 2,566,682, there is disclosed a novel formofinitiating device for setting off explosives in a well. That devicecomprised a weighted member which was adapted to slide down a cable fromwhich an explosive was suspended in a well and to close an electricalinitiating circuit to the explosive by impact of a firing pinretractably mounted in the sliding member upon an electrical contactmounted on the suspending cable and connected to the fuse of theexplosive. The sliding member was provided with a source of electricalcurrent, either self-contained or externally supplied, which fiowedthrough the firing pin when the latter made contact with the aforesaidstationary electrical contact. While this initiating device has provenquite successful in actual use, instances have occurred where a foreignobject such as a rock or rag or other electrically nonconductive objectwill accidentally become interposed between the stationary electricalcontact and the firing pin on the sliding contact and will prevent thesetting-off of the explosive charge. If, however, an attempt is thenmade to withdraw the cable carrying the explosive charge and theinitiating mechanism in order to make a fresh start, the interposedobject may become dislodged at some point along the path of withdrawaland permit closure of the contact, with the result that the explosivecharge may be set off in the well at some point other than originallyselected and consequently cause undesired damage to the well or itscasing. Also if this accidental firing should occur at or near the mouthof the well, there would be great hazard to the equipment at the top ofthe well and to the men engaged in the operations.

In other instances, the shock of the impact of the sliding member on thestationary contact member may cause the firing pin to rebound so sharplyas to break the circuit too quickly to permit transmission of therequisite firing current. Moreover, in the embodiment employing dry cellbatteries mounted in the sliding contact to supply the current, theforce of the recoil of the firing pin may be great enough to collapsethe batteries or so damage them as to make their removal for replacementpurposes costly and time-consuming.

Accordingly, a principal object of the present invention is to providean improved form of initiating device for explosives in a well whichin-- cludes features which overcome the above described defects.

An important object is the provision of means for forcibly separatingthe contact members in the event of a mis-fire in order to assure apositive break in the electrical circuit to the explosive charge.

Another object is to provide more effective and positive contact of thefiring pin during closing of the firing circuit.

Other and more specific objects and advantages of this invention willbecome apparent from the following detailed description when read inconjunction with the accompanying drawings which illustrate oneembodiment in accordance with this invention.

In the drawings:

Fig. l is a longitudinal sectional view through an initiating device inaccordance with an embodiment of this invention, showing the parts ofthe device in the normal circuit-closing position;

Fig. 2 is an elevational view, partly in section, of a portion of thedevice illustrating another position of some of theelements of thedevice;

Fig. 3 is a cross-sectional view along line 3-3 of Fig. 1; and

Fig. 4 is a longitudinal sectional view of a well showing the relativepositions therein of an explosive charge and the initiating device atthe stage of operation corresponding to that illustrated in Fig. 1.

Referring to the drawings and first to Fig. 4, there is shown a wellbore lined with a casing ID. A wire line or cable ll extends into thewell and has suspended from the lower end thereof a container l2 adaptedto enclose an explosive charge and provided with an electrical detonatorfuse, indicated by the numeral 13, which is of any suitable orconventional form for detonating the explosive charge in container [2. Astationary electrical contact, designated generally by the numeral 14,is mounted on cable H a substantial distance above container l2 and istightly clamped to the cable by means of clamping screws l5. Anelectrical conductor lead It extends from stationary contact M to fusel3. Slidably mounted on cable I I is a sliding contact member,designated generally by the numeral I1, carrying a firing pin l8extending from its lower end and adapted to close the electrical circuitto fuse [3 when firing pin l8 comes in contact with stationary contactI4.

Stationary contact member l l comprises a metallic block 20 having alongitudinal bore 2| through which cable Il may be inserted and tightlyclamped therein by means of clamping screws 15. Seated in the upper endof block 20 is an insulating block 22 in the upper face of which isembedded an annular contact ring 23, concentrically surrounding cablell. Contact ring 23 is constructed of copper or any other suitableelectrically conductive metal. Conductor lead [6 is threaded through asuitable bore 24 in blocks 20 and 22 and is connected to contact ring23.

Sliding contact I! comprises a generally cylindrical body 25 which ispreferablyv constructed of steel or other heavy electrically conductingmetal, and is provided with a removable head 26 of similar heavy metal,in order that body 25 will have substantial weight sufficient toovercome the buoyancy afiect of any of the fluids normally present inwells in which the device is conventionally run. Body 25 and head 26 areprovided with a longitudinal slot 2'! which extends radially from theaxis of the body to the exterior thereof in which cable H may belaterally inserted when the sliding contact is to be mounted on thecable. Longitudinally spaced keeper pins 23 extend laterally throughbody 25 across slot 21 to hold body 25 on the cable while permitting thebody to slide freely thereon.

Body 25 is bored longitudinally at one side to form a batterychamber'zii in which a battery 39, such as a conventional dry cellbattery, may be inserted with its positive terminal 31 downwardlydirected. The metal case of the battery, which is its negative terminal,is arranged to be in contact with the wall of chamber 29 and with head28 when the latter is connected to the upper end of body 25, asillustrated. A passageway 32 of somewhat smaller diameter than chamber29- forms an extension of the latter to a point adlament the lower endof body 25 where an opening 33 of still smaller diameter is provided forthe reception of firing pin 13. Passageway 32 is provided with aninsulating liner 34. Slidably mounted in liner 3% is a piston 35,constructed of insulating material, through which the upper end offiring pin 18 extends. The portion of firing pin 58 which extendsthrough opening 33 is enclosed in an insulating sleeve 36. The inner endof firing pin is is electrically connected by means of a flexibleelectrical conductor 31 to a metal washer 38 mounted transversely ininsulating sleeve 34 and pressed against the positive battery terminal 3i by a coil compression spring 39. Electrical connection between firingpin l8 and positive terminal 3| is thus established, while, by means ofinsulating elements 34, 35 and 35, the firing pin is insulated from thenegative side of the battery and its extensions, as represented by body25. Head 26 is provided with a metal detent 49 which presses againstcable I I and is slidable thereon to assure good electrical contactbetween the sliding contact and the cable, the latter forming the groundconnection for the electrical circuit. Spaced from chamber 29, body 25is bored longitudinally throughout its length to provide a passageway4i, and head 26 is likewise provided with a registering passageway 42 ofslightly smaller diameter than passageway 4i. Slidably inserted inpassageways M and 42 is an elongated rod d3 of greater length than thecombined length of passageways 4i and 42 to thereby extend for anappreciable distance above the upper end of head 26, when rod 43 hasbeen fully inserted within passageways 4| and 42. The upper end of rod43 is provided with a knob 44 adapted to form a striking surface for theupper end of the rod. The lower end of rod 43 is provided with a head 45which, at the point of connection with rod 43 is enlarged toapproximately the diameter of passageway 4| to form a shoulder ii; aboutthe lower end of rod 43. A coil spring :3! is mounted in passageway 4|encircling rod 43 and is held in compression between head 26 andshoulder 41. Head 45 may be pointed at its lower end, as at 8, and isprovided at an intermediate point thereof with a transverse of opening49 which is adapted to receive a shear pin B which is adapted to beinserted laterally through a suitable opening in body 25 into opening49. Shear pin 50 is provided with a threaded head 5| for engagingsuitable threads in the body opening through which the shear pin isinserted. Opening 59 is so placed with reference to the lower end ofhead 45 that the latter will be held fully retracted inside body 25 whenshear pin 50 is in place in opening 49.

Theabove described device is employed in the following manner fordetonating explosives: Stationary contact It will be threaded over theend of cable l I and firmly clamped in place at a desired distance abovethe lower end of the cable. Container l2 and its enclosed explosivecharge will be tied to the end of the cable and conductor it connectedto fuse l2. The cable carrying these elements will then be lowered intocasing Ii] until it attains the desired depth therein. Sliding contactI! will then be mounted on the cableat the top of the well and releasedto slide down the cable. When firing pin I8 strikes contact ring 23, theelectrical circuit between battery 3G and the fuse will be closed andcurrent will flow to detonate thefuse and set off the main explosivecharge. When firing pin 58 strikes contact ring 2.3, the pin will recoilin passageway 32. However, coil spring 3? will absorb the shock of thisrecoil and prevent its transmission to the end of the battery therebyprotecting the latter against batteringby the inner end of the firingpin. At the same time ,coil spring 3'? will tend to slow up the recoilof the firing pin and so act to maintain contact of the pin with contactring 23 for a time suflicienttopermit adequate flow of firing currentthrough the circuit. This will constitute the normal operation of thedevice and when the explosive has been set-oii, cable II will bewithdrawn from the well bringing with it sliding contact ii andstationary contact i4, since the latter will normally be positioned oncable ll far enough above container [2 as to remain undamaged by theexplosion. Thus the initiating device can be re-used as often asrequired for setting oif additional charges of explosives. Onlyoccasional replacement of battery 36 will be required to restore thedevice to full operative condition.

In those cases where a mis-fire may occur, as by a rag or otherelectrically non-conductive object becoming interposed between contactring 23 and firing pin 18, it will be necessary to withdraw the entirefiring string including the explosive charge from the well. In orderthat this may be accomplished with complete safety, the followingprocedure may be employed: A weighted object 52, indicated in brokenoutlines in Fig. 4, such as an iron block, will be slidably mounted oncable H and will be released to slide down the cable and forcibly strikeknob M. This will drive rod 43 downwardly with sufiicient force to breakshear pin 58 and drive the rod through body 25 and. cause the lower endof head 45 to strike contact ring 23. Body 25 will rebound upwardly awayfrom contact ring and will be urged in this reverse movement by coilspring 41, which is normally chosen of such strength as to fully supporta weight in excess of that of sliding contact l'l, as a whole. This willcause head 35 to protrude from body 25 for a distance greater than thelength of firing 'pin l8, so that with the retraction of sliding contactI! on rod 43, the firing pin will be pulled completely away from itscontact with contact ring 23 and as contact I! will be held in thisretracted position by the strength of coil spring 41, the electricalcircuit to the exhmllllllltllllll plosive charge will be completelybroken and maintained in this broken condition so that the firing stringmay now be withdrawn from the well with complete safety. If for anyreason firing pin [8 should not be pulled completely away from contactring 23, despite the contact of head 45 with the contact ring, thelatter contact will in any event create a short circuit in the firingcircuit which will prevent transmission of battery current to the fuseand so render the device safe for removal.

It will be understood that various changes and alternations may be madein the details of the above-described illustrative embodiment of thisinvention without departing from the scope of the appended claims butwithin the spirit of this invention.

What I claim and desire to secure by Letters Patent is:

1. An electrical initiator for setting olT an explosive charge in awell, comprising in combination with a cable for suspending an explosivecharge in a well, a carrier slidable on said cable, an electricaldetonator adapted to be connected to said charge and having a contactmounted on said cable in the path of said carrier, a source of electriccurrent mounted on said carrier, a second contact connected to saidcurrent source and mounted on said carrier to engage the detonatorcontact upon impact therewith of said carrier to thereby place saiddetonator in circuit with said current source, and a plunger memberyieldably retained within said carrier and projectible therefrom bypercussive force into engagement with said detonator contact.

2. An electrical initiator for setting off an explosive charge in awell, comprising in combination with a cable for suspending an explosivecharge in a well, a carrier having a guide for movement along saidcable, an electrical detonator adapted to be connected to said chargeand having a contact mounted on said cable in the path of said carrier,a source of electric current mounted on said carrier, a contactconnected to said current source and mounted on said carrier to engagethe detonator contact upon impact therewith of said carrier to therebyplace said detonator in circuit with said current source, and a plungermember yieldably retained Within said carrier and projectible therefromby percussive force into engagement with said detonator contact.

3. An electrical initiator for setting off an explosive charge in awell, comprising in combination with a cable for suspending an explosivecharge in a well, a carrier having a guide for movement along saidcable, an electrical detonator adapted to be connected to said chargeand having a contact mounted on said cable in the path of said carrier,a source of electric current mounted on said carrier, a movable firingpin electrically connected to said source normally extending from saidcarrier to engage the detonator contact upon impact therewith to therebyplace said detonator in circuit with said current source,recoil-absorbing means in said carrier connected to said firing pin, anda plunger member yieldably retained within said carrier and projectibletherefrom by percussive force into engagement with said detonatorcontact.

l. An electrical initiator for setting off an explosive charge in awell, comprising in combination with a cable for suspending an explosivecharge in a well, a carrier slidable on said cable.

an electrical detonator adapted to be connected to said charge andhaving a contact mounted on said cable in the path of said carrier, aself-contained source of electric current enclosed within said carrier,a firing contact connected to said current source and mounted on saidcarrier to engage the detonator contact upon impact therewith of saidcarrier to thereby place said detonator in circuit with said currentsource, and a plunger member yieldably retained within said carrier andprojectible therefrom by percussive force into engagement with saiddetonator contact.

5. An electrical initiator for setting off an explosive charge in awell, comprising in combination with a cable for suspending an explosivecharge in a well, a carrier slidable on said cable, an electricaldetonator adapted to be connected to said charge and having a contactmounted on said cable in the path of said carrier, a self-containedsource of electric current enclosed within said carrier, a firingcontact connected to said current source and yieldably extending fromsaid carrier to engage the detonator contact upon impact therewith ofsaid carrier to thereby place said detonator in circuit with saidcurrent source, plunger means longitudinally slidable in said carrier,resilient means normally urging said plunger means downwardly out ofsaid carrier, retaining means normally holding said plunger means withinsaid body and releasable by percussive impact on the upper end of saidplunger means to release said plunger means for forcible impact uponsaid detonator contact to thereby cause retraction of said carrier fromengagement with said detonator contact.

6. An electrical initiator for setting off an explosive charge in awell, comprising in combination with a cable for suspending an explosivecharge in a Well, a cylindrical carrier having a guide for downwardmovement on said cable, an electrical initiator adapted to be connectedto said charge and having a contact mounted on said cable in the path ofsaid carrier, a movable firing pin protruding from the lower end thereoffor engagement with said contact to place said detonator in circuit withsaid current source, a selfcontained source of electric current enclosedwithin said carrier connected to said firing pin, a recoil-absorbingspring mounted in said carrier in engagement with said firing pin, anelongated plunger slidably mounted longitudinally of said carrier andextending from the upper end thereof, spring means engaged between saidcarrier and said plunger normally urging the plunger downwardly out ofsaid carrier, a shear pin arranged in said carrier to hold said plungerretracted within said carrier,-said shear pin being breakable bypercussive impact on the upper end of said plunger to release same forforcible impact upon said contact.

WILLIAM G. SWEETMAN.

REFERENCES CKTED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 341,536 Zalinski May 11, 18861,273,825 Coby et a1 July 30, 1918 1,458,925 Barab June 19, 19232,059,488 Prikel Nov. 3, 1936 2,390,676 Alexander Dec. 11, 194.5

